1. Field of the Invention
The present invention relates to laser beam steering systems. In particular, the present invention relates to an all-reflective coarse-steering element designed to conformally fit or to be flushly integrated in a modular manner with the outer surface of a body of a vehicle such as an aircraft, spacecraft, ocean vessel, land conveyance vehicle or the like.
2. Background of the Invention
Precise and controllable delivery of laser beams to a desired location is an important technology with respect to telecommunications, military, and other general industrial applications. The most common means of obtaining such delivery is the use of large (i.e. macroscopic) mechanically controlled mirrors, lenses and gimbals to steer laser beams. While this technology is mature, it is limited by the mechanical nature of mirror movement. Furthermore, inertial properties of mechanically driven mirrors limit the speed with which steering can be changed.
There are numerous new beam-steering applications which have been identified; however, current beam-steering technology does not exist to support such identified applications. For instance, in the near term, new technologies for beam-steering systems must facilitate self-protection [techniques-based infrared countermeasures (IRCM)], targeting, passive and active searching and tracking, and free-space optical (FSO) communications. These systems must accommodate, in the longer term, damage-and-degrade-based (D2) infrared countermeasures. The new beam-steering technologies must also be “conformal” to the outer skin of a vehicle, such as an aircraft, in order to reduce aerodynamic drag, reduce radar cross section, and minimize the obscuration to adjacent electro-optic (EO) systems.
These aforementioned emerging approaches are often referred to as “non-gimbal based” technologies. Numerous approaches have been funded through government programs including STAB (“Steered Agile Beams”), MEDUSA (“Multi-function Electro-Optics for Defense of US Aircraft”), THOR (TeraHertz Operational Reachback”), CCIT (Coherent Communications, Imaging, and Targeting”). Approaches involving rotating-prisms, flexible waveguides, liquid-crystals (LC), MEMs-based deformable mirrors (DM), acousto-optics, and other technologies are presently being funded.
Among both known and emerging approaches, none presently meet or are forecasted to meet the following specifications, within reasonable size, weight, and power requirements (SWAP): (1) the ability to be installed conformally with the skin of a vehicle, and still achieve a steering field of regard (FOR) of 180° Az and +/−45° El.; (2) the ability to maintain achromaticity over the range of 1 μm<λ<12 μm; and (3) the ability to maintain both coherence and phase across the wavefront.
For example, approaches that are not based on all-reflective optics can generate some level of pointing error when steering two different wavelengths (achromaticity). Further, a general problem with array-based agile designs is that they can disrupt the phase uniformity of the wavefront, leading to problems in coherent-imaging schemes, as well as temporal spreading of the pulse in FSO-communications designs [i.e., the true-time delay (TTD) problem].
Other approaches have been suggested which would utilize existing technologies, such as a ball-turret (see FIG. 3 for an example of prior art electro-optic ball-turret) recessed into the vehicle body. However, the downside of this approach is that to obtain a full field of regard (FOR) a large window is required. This approach is further not feasible because the ball-turret must be deeply recessed and positioned within the body of the vehicle. Such an approach would simply utilize too much space within the vehicle.
Another approach that has been suggested as a conformal package is to implement a rotating prisms concept, which utilizes two prisms that rotate against each other. However, this approach is not desirable because the system is not entirely reflective, and as a result, there is a pointing error among different colors of the spectrum.
One approach that can be successfully implemented to meet the aforementioned requirements [(1) ability to be installed conformally with the skin of a vehicle, and still achieve a steering field of regard (FOR) of 180° Az and +/−45° El.; (2) maintenance of achromaticity over the range of 1 μm<λ<12 μm; and (3) maintenance of both coherence and phase across the wavefront] is to provide an electro-optical system having all upstream off-gimbal components except for the coarse-steering element. For instance, the design may incorporate modern technologies such as adaptive optics for the fine-steering elements, however, the final coarse-steering element will utilize conventional mirror and gimbal technology. However, currently to date, no embodiments of the aforementioned concept have been successfully reduced to practice.
Thus, overall, in order to support multifunctional electro-optical missions, it would be advantageous and desirable to provide an ideal beam-steering device which would be both conformal and all-reflective. Such a device potentially could be used in a multi-functional manner for self-protection and FSO-communications missions, for example. Furthermore, it would be desirable to provide a coarse-steering element which is compact in size and of which has a smaller window profile. In particular, it would be beneficial to provide a final coarse-steering element, such as a one-tilt mirror gimbal assembly, which may be positioned very close to the exit pupil window of the EO system such that a conformal all-reflective design may be accomplished with a reasonable SWAP (size, weight and power). Additionally, it would be advantageous to package the entire optical device into a modular configuration such that it will meet specific modularity requirements set forth for upcoming military programs.